This enables a particularly high ratio of durability/weight to be achieved. Moreover, any kind of structure can be created, for instance, suspension components can be optimally designed for external loads. However, these adjustments also change the overall vehicle dynamics. The vehicle behaves completely differently due to the influence of the center of gravity, a changed mass-damper system, and the modified forced excitations by the drive motor.
Electric foil strain gauges from HBM are used for chassis development and optimization. They help estimate the force effect.
The basic aim is to find an optimal design – minimum weight while ensuring full operational safety.
Therefore, the wishbone tubes are being optimized. Different diameters (17-22 mm) with different tube thicknesses (1-2 mm) and lengths are being investigated. The force flow into the monocoque varies depending on the tube length.
These days, development processes are largely characterized by data exchange between simulation and real-life tests. A key factor in this is that simulation and real-life tests mutually improve the model. The resulting model safely enables a broader, more comprehensive use of simulation, which in turn saves time and costs. This facilitates mapping of the load cases as realistically as possible in the simulation, based on the known real-life forces, thus improving future developments.
Using the example of a wishbone, the interaction of simulation and real-life tests (digital twin) is to be shown.
The wishbones are loaded in the chassis as pure tension-compression rods.
1 The first step is to use the tire data to determine traction and maximum tire grip in various driving conditions. Apart from the tires, the assembly space (rim, wheel carrier, etc.), including the dampers and the chassis, are taken into account.
2 A simulative "crash analysis" is also necessary to ensure that the motors do not touch the wishbone during vehicle movement (compression, rolling, etc.) and that the tie rod does not touch the rim during steering. Furthermore, the optimum ratio of wheel suspension travel to damper travel is sought. In this simulation, different load cases that affect the chassis are also simulated. For example:
4 The CFRP tubes are dimensioned with a safety factor according to the forces calculated from the simulation. The tube length, the force acting on it, and, if necessary, a torque are entered at the far right. Different CFRP tubes can subsequently be compared depending on the outer and inner diameters to determine a design for use in the real-life test.
The wishbones fitted with strain gauges are then adjusted on a universal tension-compression testing machine.
7 The wishbones used here are adjusted to up to 1 kN. Their ball-bearing support ensures an optimal clamping position (no tension of the components due to self-alignment). The bridge output voltage values (see further information on the Wheatstone bridge circuit LINK) are compared with the forces measured using the tension-compression testing machine.
9 The wishbones fitted with strain gauges are then installed in the vehicle. The entire measuring chain consists of a 16-channel QuantumX MX1615B module, which is attached to the vehicle. The strain gauges are connected via cables using 4-wire technology. The measured data is stored on a CX22 data recorder. All measured data is synchronized via PTP2 for ease of evaluation. The strain gauges should be covered before their use in the field. ABM75 is ideal for this.
10 Finally, the real-life load data is recorded through the road test. This includes an evaluation of whether the components and the vehicle system offer adequate operational durability and how high the load is on each of the components.
Eventually, this data is used to improve component simulation:
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